APPEAL July '14Tony Weidberg, Oxford University1 Introduction To Particle Physics Why do we need accelerators and detectors? Particle Detectors with examples. Standard Model of Particle Physics Introduction to the Higgs The future Or Everything you wanted to know about the Higgs particle … but were afraid to ask

2 Why do we need Accelerators(1) Why can’t the lion see the rabbit but it can hear it? HGS November '12Tony Weidberg, Oxford University

3 Why do we need Accelerators(2) To study an object of size R, need resolution much better than R  wavelength of probe <R.  Optical microscopes resolution limited ~  m but we need resolution of ~ m to study quarks. Quantum mechanics says =h/p (h =Plank’s constant, p=momentum).  High energy/momentum particles to study structure of matter at smallest scales. HGS November '12Tony Weidberg, Oxford University

4 Particle Detectors Everybody has examples of particle detectors at home Examples are … APPEAL July '14Tony Weidberg, Oxford University

5 Particle Detectors To detect high energy particles we can use ionisation. High energy particle knocks electrons out of atoms  electrons and positive ions. Detect resulting electrons. APPEAL July '14Tony Weidberg, Oxford University

6 Wire Chambers APPEAL July '14Tony Weidberg, Oxford University

7 Scintillation Counters APPEAL July '14Tony Weidberg, Oxford University

Example: Silicon Detector High energy charged particle knocks out electrons (-ive) +ive and –ive charges move in opposite directions because of applied electric field. Resulting current measured by electronics. This is the principle behind the camera on your phone 20th June 2014Tony Weidberg, Oxford University8

9APPEAL July '14Tony Weidberg, Oxford University

10 ATLAS Si detector Oxford APPEAL July '14Tony Weidberg, Oxford University

Standard Model Particle Physics APPEAL July '14Tony Weidberg, Oxford University11

How do we know all these particles exist ? Experiments ! Electron is easy measure e/m Quarks confined in hadrons  more difficult. How about unstable particles? –Take Z 0 as an example t~ s. APPEAL July '14Tony Weidberg, Oxford University12

13 Discovery of Nucleus Experiment Fire alpha particles at thin foils and look at angle of scattering. Graduate student eye Microscope ZnS screen foil  HGS November '12Tony Weidberg, Oxford University

14 Discovery of Nucleus Theory Rutherford found that most collisions were at small angles but occasionally the  particles would bounce back. “it was as if you fired 15” shells at tissue paper and they bounced back and hit you” Nucleus electron Positive charge all inside small nucleus  large angle scatters. HGS November '12Tony Weidberg, Oxford University

15 30 GeV e - in 820 GeV p in Large angle e - scattering event in ZEUS HGS November '12Tony Weidberg, Oxford University

16 Structure of the proton Proton R ~ m  high energy probes e.g. electrons Proton appears to be made up of point like constituents: quarks Electromagnetic interaction = exchange of virtual photons. e-e- e-e- quarks  HGS November '12Tony Weidberg, Oxford University

Z 0 decays Reconstruct decay products e.g. Z  e + e - Boost to CMS Use E=mc 2 APPEAL July '14Tony Weidberg, Oxford University17

18 Origin of Mass Consider Feynman’s wheelbarrow experiment: –Put ball in wheelbarrow, push it forward and stop suddenly. –The ball continues to move forward and rolls out. Why ??? APPEAL July '14Tony Weidberg, Oxford University

19 Origin of Mass(2) So classical mechanics doesn’t explain origin of mass. Quantum theory predicts masses of all particles should be 0 ! Need to understand quantum vacuum –What is left in a bottle after I remove all the molecules? –Remember Heisenberg  E  t > h –Why does this matter? APPEAL July '14Tony Weidberg, Oxford University

Quantum Vacuum Can measure small changes in atomic energy levels, magnetic moments etc.  agree with theory. Macroscopic example: Casimir force E in < E out why? Creates inward pressure. APPEAL July '14Tony Weidberg, Oxford University20 E in E out

Higgs Vacuum Vacuum is lowest energy state of fields Average value of Higgs field non-zero. Particles interact with this field acquire mass. Can we test this theory? Yes we can Put enough energy in to create a Higgs boson. APPEAL July '14Tony Weidberg, Oxford University21

Higgs hunting How would we know if we made a Higgs boson? Use good old E=mc 2 Measure energies of decay products  reconstruct m H. APPEAL July '14Tony Weidberg, Oxford University22

Higgs Hunting Look for Higgs decaying to two photons and reconstruct Higgs mass E=mc 2reconstruct Higgs mass Evidence for Higgs boson also seen in other decay modes (ZZ and WW). How do we know the signal is real and not just a statistical fluctuation? Calculate probability of a fluctuation producing a larger signalprobability APPEAL July '14Tony Weidberg, Oxford University23

APPEAL July '14Tony Weidberg, Oxford University24

Higgs Signal  APPEAL July '14Tony Weidberg, Oxford University25

Statistical Evidence APPEAL July '14Tony Weidberg, Oxford University26

Outlook APPEAL July '14Tony Weidberg, Oxford University27 We have definitely discovered a new boson but is it the Standard Model Higgs? Measurements of spin=0 suggest it is a Higgs boson but is it SM or exotic? Need much more data …

28 Q. Why do Particle Physics? Answer: because it is interesting ! fundamental questions of what the Universe is made of and how it interacts. Towards a T.O.E. Also help to explain how the Universe evolved. Dark Matter APPEAL July '14Tony Weidberg, Oxford University

29 Other Benefits of Particle Physics Many important applications of technology developed for Particle Physics are used. Ion beam accelerators required in semiconductor industry. Synchrotron radiation –By-product of particle accelerators. Accelerators used in hospitals to produce radio- isotopes. Medical imaging (e.g. PET). Safe transformation of nuclear waste. World Wide Web invented at CERN (by Oxford Physics graduate). APPEAL July '14Tony Weidberg, Oxford University

Accelerators Use E=mc 2 What does this mean? We know Higgs mass m H >115 GeV/c 2 Need very high energy particle accelerator: –LHC centre of mass proton – proton collisions 7 to 8 TeV (upgrade to 14 TeV). –1 TeV = eV: 1 eV is energy given to an electron by a 1V battery APPEAL July '14Tony Weidberg, Oxford University30

31 Particle Accelerators Everybody has a particle accelerator at home. It is called a … APPEAL July '14Tony Weidberg, Oxford University

32 TV = Electron Accelerators APPEAL July '14Tony Weidberg, Oxford University

33 Circular Accelerators APPEAL July '14Tony Weidberg, Oxford University

34APPEAL July '14Tony Weidberg, Oxford University

35 Superconducting Magnets APPEAL July '14Tony Weidberg, Oxford University

Superconducting Magnets 9T for the LHC APPEAL July '14Tony Weidberg, Oxford University

37 Superconducting RF Cavity APPEAL July '14Tony Weidberg, Oxford University

38 4 Si Barrels Assembled APPEAL July '14Tony Weidberg, Oxford University

39 Detector Challenges 10 9 interactions/second Select ~10 3 interesting events from background of Makes finding finding a needle in a haytsack look like a piece of cake. APPEAL July '14Tony Weidberg, Oxford University

40 ATLAS Torroid Magnets APPEAL July '14Tony Weidberg, Oxford University